Technical Field
Embodiments of the subject matter disclosed herein generally relate to seismic acquisition systems, devices and methods, and more specifically to management and testing of such systems.
Discussion of the Background
Seismic waves generated artificially for the imaging of geological layers have been used for many years. Reflection seismology is a method of geophysical exploration used to determine the properties of a portion of a subsurface layer in the earth, which information is especially helpful in the oil and gas industry. Seismic waves (i.e., sound or other pressure waves) are sent into the earth, directed toward the subsurface area. Seismic data are collected regarding the time it takes for the reflections of the generated seismic waves to come back to one or more receivers. Reflections are generally representative of interfaces between the layers of the subsurface. The seismic data can therefore be analyzed to generate a profile (image) of the geophysical structure, i.e., the layers of the investigated subsurface. This type of seismic acquisition or exploration can be used both on the subsurface of land areas and for exploring the subsurface of the ocean floor. For example, marine techniques send energy waves into the earth by first generating the energy waves in or on the ocean.
One way to perform marine seismic acquisitions or surveys is to tow an array of seismic receivers, which may be disposed on elongated streamers, by a vessel over the geographical area of interest (GAI) and to generate source signals with one or more sources (towed by said vessel or a dedicated vessel which tows only the sources), and receive corresponding reflections while traversing the GAI. This process is sometimes referred to as “shooting” a GAI or cell being surveyed.
As marine seismic surveying has increased in sophistication, it has become possible to tow more sources and receivers behind a single vessel. Streamers can now be up to 18 km long, towed at approximately 5 knots, 10 m below the ocean surface. In addition to sources or receivers, streamers can include “birds” with control surfaces used to position the streamer vertically or horizontally. Streamers can also include other components such as in-sea modules that process seismic data, recover modules, mammals detection modules, ranging modules, etc.
Given the length of streamers, they are generally stored spooled on winches on the back of the vessel when not in use. For example, a storage winch can hold up to 18 km of a streamer having a diameter up to 60 mm. Furthermore, components of streamers are often detachable from each other. This permits reconfiguring a streamer to include the number of positioning elements (e.g., birds), receivers, noise cancelling sections or other elements required to shoot a particular GAI. In this respect, note that a streamer may include tens if not hundreds of components that can be arranged in many different ways to form the streamer. Therefore, once a streamer is placed on a spool, it is very difficult to identify each component of the streamer and decide whether the streamer has the correct configuration for a next seismic survey. Even more, after a seismic survey is finalized and the vessel is deployed for another seismic survey requiring a different streamer configuration, it is logistically difficult for the vessel's operator to determine each component of the streamer for reconfiguring the streamer.
It is therefore desirable to be able to locate a particular element on a streamer to be removed or replaced while configuring streamers for a GAI, or for maintenance. It is also desirable for operators of seismic measurement systems to be able to audit their equipment inventory, e.g., their stock of streamer components. It is further desirable to be able to verify that a streamer was correctly configured.
A prior scheme for managing streamer elements includes personnel manually recording elements and their order along a streamer on paper spreadsheets. These spreadsheets are then cross-checked with design spreadsheets. However, this is time-consuming, expensive in labor, and error-prone. Another scheme involves placing radio-frequency identification (RFID) tags on one or more element(s) on a streamer. RFID-tagged components can be identified automatically during deployment of the streamer, by passing the streamer within the read range of an RFID reader, e.g., in the back deck of the vessel. Although this may help verify a streamer configuration, scanning RFID tags during deployment of the streamer does not help with the process of assembling the streamer including the correct elements in the correct order. In other words, if the RFID scanning is performed when the streamer is still on the spool, a topology of the streamer cannot be detected. Moreover, when a streamer is wound on a winch, RFID signals from components closer to the axis of the winch can be distorted or attenuated by components farther from the axis of the winch, and information about the elements is lost. Current schemes use manual recordkeeping for equipment on winches, which recordkeeping is time-consuming and error-prone. Accordingly, there is a continuing need for ways of accurately determining the elements present on a seismic line, and their order, even when the streamer is on the spool in the back of the vessel. There is a further need for ways of locating faulty components on a streamer.